The invention relates to a toothed belt for transporting objects including a band-shaped belt body, which carries teeth formed on one side, at least one of the teeth being provided with at least one opening, which extends from the crown surface of the associated tooth through the toothed belt to the other side of the belt body and in which a retaining element for an object holder to be fastened to the other side of the belt body is arranged.
Such toothed belts are commonly used in production lines in which they are used for transporting workpieces from one processing station to another. This can be effected in a continuous movement or in a reciprocating movement.
Toothed belts offer the advantage of very precise movement control and thus very precise positioning of the object holders at the loading and unloading stations. The object holders ensure that the workpieces are reliably transported and remain precisely aligned.
The object holders were previously clamped against the rear surface of the toothed belt using screws which were screwed into the retaining elements. The latter were nuts which were situated in the associated openings at the height of the teeth. The openings defined a step at the height of the tooth feet, on which the retaining elements rested. The openings then continued through the belt body with a reduced diameter.
It has been found that the transport precision of such toothed belts, which are known in practice, leaves something to be desired.
It is thus the object of the invention to provide a toothed belt with increased transport accuracy.
In order to solve this object the toothed belt referred to above is characterised in accordance with the invention in that the retaining element has an elongate body which extends through the tooth at least into the belt body,
that the elongate body has a head in the form of at least one laterally projecting wing and
that the wing engages in a broadened region of the opening which is formed in the crown surface of the tooth.
The invention is based on the recognition that in the previously known toothed transport belts loosening of the object mountings was due to the fact that the nuts disposed in the openings provided too short a screw-in length by reason of their small dimensions. This risk is eliminated by the retaining elements in accordance with the invention.
The elongate body of the retaining elements, which extends at least into the belt body, provides sufficient substance to ensure a reliable fastening of the object mounting. This applies regardless of the shape of the elongate body.
The elongate body of the retaining element is preferably constructed in the form of a sleeve. The sleeve provides a sufficient engagement length. This applies particularly when the opening extends through the entire retaining element in the form of a through-opening. The engagement length results from the sum of the height of the tooth and the length of the elongate body which extends into the belt body.
The sleeves are preferably provided with an internal screwthread over their entire length. This is particularly appropriate when the sleeves consist of metal. In an important further embodiment of the invention it is proposed that the retaining elements be made of plastics material, preferably of glass fibre-reinforced polyamide. Plastics material of sufficient strength and hardness is readily able to cope with the requirements placed on the retaining elements. Plastics material offers, above all, the advantage that damage of the toothed pulleys cooperating with the toothed belts is reliably prevented.
The toothed belt preferably also comprises plastics material, particularly polyurethane, whereby longitudinally extending reinforcing wire cables are inserted in the belt body at the junction with the teeth. Such a toothed belt has proved to be satisfactory as regards the precision of its movement control. Polyurethane is high temperature-resistant. The same applies to the retaining elements of glass fibre-reinforced polyamide.
Sleeves of plastic material offer the further advantage that an internal screwthread can be omitted. The screwthread is pressed into the sleeve by the self-tapping screw, when it is screwed in. Furthermore, retaining elements of plastics material are lighter than metal sleeves.
The precision of the positioning of the workpieces, both at the loading station and at the unloading station, is determined by the precise arrangement of the openings in the toothed belt and the precise fastening of the object mountings with respect to these openings. In order to promote the latter aspect, it is proposed in a further embodiment of the invention that the elongate body of the retaining element engages through the belt body and projects out of its other side. The elongate body thus constitutes a centering projection on the rear surface of the belt which makes optimal positioning and alignment of the object mountings possible and, when the object mountings are secured by adhesive, can also serve as a jointing aid to reduce the mounting times.
The openings in the toothed belt can be produced subsequent to its manufacture. Optimal accuracy is obtained when the production of the openings is integrated into the moulding process of the toothed belt. The moulding process also ensures the desired spacing accuracy. The moulding process also offers the possibility of cutting a plurality of toothed belts of the desired breadth from an appropriate moulded article.
If the elongate body of the retaining element is of sleeve-shaped construction, its end projecting out of the other side of the belt body constitutes the centering projection which is of annular construction and permits the screwing in of a screw. It is proposed in a further embodiment of the invention that fastening or locking means be provided at this end of the elongate body. A sleeve-shaped construction is possible but not absolutely necessary. Also possible, for instance, is a threaded peg for the screwing on of a nut. The retaining element can also be provided with an elastic locking mechanism for engaging in the object mounting, for instance in the form of a head which is split or constructed to be elastic in some other manner.
The wing of the retaining element ensures that when the object mountings are tightened the mounting element cannot be drawn into the material of the toothed belt. This also increases the fastening security of the object mountings. This effect may be readily intensified if the head of the retaining element is constituted by two projecting wings which are diametrically opposed to one another. The wings extend on both sides of the elongate body in the longitudinal direction of the associated tooth and thus offer a large, force-balanced reaction surface, whereby they simultaneously ensure the rotational security of the retaining element. The wings preferably extend over the region of wire reinforcing cables which are embedded in the belt body.
The arrangement is such that the elongate body and its head are situated within the contour of the tooth and thus cannot impair the mode of operation of the tooth. In general, the outer diameter of the elongate body, which defines the breadth of the head, will be so selected that it corresponds exactly to the breadth of the crown of the tooth. It is then particularly advantageous to construct the wings of substantially triangular shape so that they fit harmoniously into the outline of the crown of the tooth. Rectangular wings are, however, equally possible, particularly if the elongate body has a relatively small outer diameter.
It is proposed in an important further embodiment of the invention that the head of the elongate body is fitted into the broadened region of the opening. The retaining element thus terminates with the plane of the crown surface of the tooth, whereby its wings adjoin the wall of the opening with practically no gap. The large advantage of this construction resides in the fact that the retaining element, which is suitable for transmitting shear forces, substantially replaces that material which was removed from the toothed belt to form the opening. The opening thus no longer constitutes a weak point in the tooth. This means that large forces can still be transmitted. In this connection, it is also possible to provide one and the same tooth with a plurality of fastening points.
Furthermore, the fit of the opening and retaining element can be so selected that the retaining element can be pushed into the opening and is frictionally secured therein against falling out, even if it is not held in place by the clamping of an object mounting.
The possibility is thus offered of equipping the toothed belt with a plurality of fastening points so that the user may use the toothed belt in very many ways. There is thus the possibility of experimentally determining the optimal arrangement of the object mountings both transverse to the toothed belt and in its longitudinal direction. Improvisations are also possible without difficulty. In this connection, it is apparently of no importance what type of object mountings are used in the specific application. The toothed belt is thus universally usable.
If the retaining elements comprise plastics material, they are preferably produced by injection moulding. This is not only simple and economical but also permits a high degree of variability in their shape.
If the user wishes to provide only a proportion of the fastening points which are provided on the toothed belt with retaining elements, blind elements can be pushed or glued into the unused openings. The strength of the teeth is maintained under these circumstances.
Furthermore, the retaining elements and also the blind elements are interchangeable and may be replaced by elements of a different type. Breakage of the elements does not result in destruction of the toothed belt. The object mountings are also interchangeable in a variable manner and may be replaced when worn.
The invention will be described below in more detail by way of preferred embodiments with reference to the accompanying drawings.